Adding numerous different organic additives to acid electrolytic copper baths is known in order to enable the decorative and functional characteristics of the copper coatings to be controlled. Above all, brighteners and carriers are added to the baths in order to obtain bright deposits. In addition, organic compounds are used as additives to the coppering baths during the production of printed circuit boards, chip carriers and semiconductor wafers, and these compounds are to act as levelers and enable as uniform a deposition of copper as possible in and on different regions of the surface of the printed circuit board or of the structure of the printed circuit board, e.g., the trenches or the BMVs.
The uniform deposition of copper is often difficult in view of the geometric arrangement and development of the individual regions, in particular in trenches, BMVs or through vias, as these regions exhibit a variable electric depositing behaviour. In particular, in very small structures of this type (in the medium to lower μm range), influences of the diffusion of the metal ions and of the additives towards the deposition location are dominant. A uniform deposition of copper is the prerequisite for the development of complex conductor structures. Otherwise, the result can be insufficient or excessive deposition, for example, at the walls of the through vias, leading to their uselessness and consequently to the rejection of the entire printed circuit board or chip carrier. The same result is produced by insufficient and non-uniform metallisation of the trenches and BMVs on printed circuit boards, chip carriers and wafers, as in very small structures that are to be completely filled by the metal, hollow spaces (voids) form in the copper deposit or the structures can be reproduced on the surface after the coppering process due to unevenness. This makes additional operating steps and material costs necessary for building up subsequent layers and problems can arise due to impedance fluctuations that are no longer tolerable.
U.S. Pat. No. 2,876,178 describes an alkaline cyanide copper bath in which amino acids or secondary amino acid derivatives, such as peptones and peptides, are contained. These additives are said to have advantageous effects on the copper depositing process.
U.S. Pat. No. 5,215,645 describes a copper bath for the electrolytic forming of a copper foil to be used in the construction of a printed circuit board. The copper bath contains gelatine compounds along with other additives. These types of compounds are described as high-polymer proteins of amino acids with a molecular weight of from 10,000 to 300,000. According to the introduction to the description in this document, gelatine additives are used to control the roughness of the deposited copper layers. In addition, an active sulfur compound, preferably thiourea, is contained in order to limit the roughness of the deposited copper.
US 2004/0188263 A1 also describes the generation of a copper foil for the production of printed circuit boards by means of a copper bath. The bath used for this purpose contains, among other things, glue, gelatine and collagen peptide. The copper foil formed makes it easier to drill holes through the copper foil with a laser when producing printed circuit boards without requiring an auxiliary nickel metal layer for example.
The production of more efficient integrated circuits for IC chips also requires the use of more efficient copper depositing baths with corresponding bath additives, some of the abovementioned requirements having an even greater importance. P. M. Vereecken et al.: “The chemistry of additives in damascene copper plating”, IBM J. Res. & Dev., Vol. 49 (Jan. 2005), No. 1, 3-18, describes compositions containing, for example, polyether, sulfur-based organic compounds and levelers, such as thiourea, benzotriazole (BTA) and Janus Green B (JGB), with which mirror-like copper surfaces can be generated and which enable accelerated copper deposition in the finest trenches.
US 2002/0195351 A1 discloses a composition for the electrolytic deposition of copper onto integrated circuits, for example in narrow trenches for conductor paths or conductor path connections (vias). The composition contains, along with other additives, sulfur containing amino acids as polishing means, for example, cysteine, percysteine, glutathione and the derivatives and salts thereof.
U.S. Pat. No. 5,972,192 discloses a method of electroplating Cu to reliably fill openings in a dielectric layer, particularly high aspect ratio openings for contacts, vias and/or trenches. An electroplating solution is employed which comprises a leveling agent and optionally a brightening agent. The leveling agent can be selected from polyethyleneimine, polygylcine, 2-amino-1-naphthalinesulfonic acid, 3-amino-1-propanesulfonic acid, 4-aminotoluene-2-sulfonic acid and further compounds. A suitable brightening agent may be 2,5-dimercapto-1,3,4-thiodiazol.
U.S. Pat. No. 6,261,433 B1 discloses an electrochemical deposition method which is used for copper electrodeposition on semiconductor substrates. An electroplating solution is used which may include, i.a., dipeptide diaminoacid, diglycine and triglycine.
With the progressive miniaturisation of printed circuit boards or the design of printed circuit boards and wafers becoming ever more complex, with the aim, among other things, of providing greater calculating capacities and/or functionalities in an ever decreasing space, the industry is always facing new challenges. At the same time, the geometry, for example of the printed circuit boards or respectively of the conductor path structures and of the conductor structures on printed circuit boards, chip carriers and semiconductor wafers is becoming more and more complicated. For example, the ratio of the copper thickness to the width of a conductor path or respectively of the hole depth relative to the diameter of the hole (aspect ratio) is constantly becoming greater as the hole diameters are becoming smaller and smaller and the conductor paths narrower and narrower.
In particular, it has been shown that the uniformity of the metal deposition on printed circuit boards, chip carriers and semiconductor wafers using the known methods is insufficient to guarantee reliable generation of the conductor structures in trenches and vias. Due to the structures becoming smaller and smaller, a copper layer with an uneven surface is formed as the copper is being deposited. The result of this in damascene methods for the generation of conductor structures is that a reliable result for chemical/mechanical polishing can no longer be achieved without having to do more. For it is a prerequisite condition for this method step that the copper surfaces generated during the electrolytic deposition process be extensively smooth and even so that metal can be removed in a reliable manner up to the desired depth. In addition, it is clear that the desired effects do not occur with the necessary reproducibility.
To meet these requirements, there is a need for bath solutions for the accurate uniform deposition of copper, where this effect is supplied in a reproducible manner. In particular, the requirement is for bath solutions that are suitable to fill trenches and BMVs in such a manner that the formed conductor structures exhibit a uniform distribution of layer thickness and good conductivity, that the formed conductor paths, therefore, do not have a so-called ski slope shape (concave shape of the copper surface in cross-section corresponding to the rounding of a ski tip) or any other concave structures either and the BMVs do not have a so-called dimple shape (depression of the copper surface at the point of the via). At the same time, the filling characteristics of the bath solutions, such as in particular micro-throwing, must not be impaired.
The aforementioned requirements cannot be met by the previously known bath solutions. In particular, it is not possible to achieve a uniform distribution of layer thickness with the deposited copper in particular in trenches and BMVs and, in any case, this cannot be achieved in a reproducible manner.
Consequently, the problem on which the present invention is based is that the known bath solutions are not suitable to fill micro structures of through holes, trenches and BMVs with sufficient precision in a uniform manner, i.e., with a copper surface that is as even as possible. Consequently, it is the object of the present invention to solve this problem and, over and above this, to guarantee that the aforementioned requirements are constantly achievable even under the conditions of mass production.
In particular, micro structures, such as through holes, trenches and BMVs, on printed circuit boards, chip carriers and semiconductor wafers, are to be filled in such a manner that there are no disadvantageous effects, such as ski-slopes and dimples, and that an even surface with uniform layer thickness is produced overall.